For many years, rock samples have been obtained using core barrel assemblies. A diamond or carbide bit of a "doughnut" shape is connected to the outer tube of the core barrel assembly and when rotated cuts into rock. An inner tube that is bearing supported at the top is positioned just above the inner edge of the bit. The rock core sample enters the inner tube as the bit cuts the rock and advances. A drilling fluid is used to remove the cuttings at the area of the bit and transport them to the surface. The drilling fluid under pressure also prevents cuttings from entering between the core barrel inner tube and outer tube. The bearing at the top of the inner tube allows the inner tube to remain stationary as the core barrel assembly is rotated. This tends to prevent the inner, core retaining tube from rotating with the rotation of the outer tube of the core barrel, although the inner tube is not positively restrained against rotation.
The core barrel assembly can be removed after a five or ten foot run and the core removed. Another method is to remove only the inner tube, using a wireline cable. In this case, the inner tube has a latching means to lock it in its proper position within the outer tube. A bearing is also supplied between the latching means and the inner tube so that the inner tube will not rotate when the outer tube is rotated, provided that nothing binds between them.
U.S. patents illustrating such prior art barrel assemblies include Reed, U.S. Pat. Nos. 3,977,482 and Pickard, 3,120,282.
The obtaining of soil samples poses quite different problems from obtaining rock cores. Most soils are too soft to core, and in order to obtain an undisturbed sample, a thin wall tube is often pushed into the soil several feet. The soil sample is cut by the leading edge of the tube and is pushed into the sample tube. The tube is then extracted from the hole and the sample is later extruded from the tube. The hole is generally advanced using hollow stem auger or rotary drilling methods. One hollow stem auger design is covered by Rassieur U.S. Pat. No. Re. 26,938.
A hollow auger drill head is connected to the lead auger and the auger sections are connected to a drive cap that is rotated by the drill rig. In order to cut the center of the hole, a pilot assembly is positioned at the opening of the drill head and is connected to the drive cap with threaded drill rods. As the drive cap rotates, the center section and the hollow augers rotate together. It can be time consuming to remove the drill rods an pilot assembly, insert the sample tube and drill rods to obtain the sample, and to remove the sample and drill rods and reinsert the pilot assembly and rods.
Rassieur U.S. Pat. No. 3,241,624 covers a two-part rotary cutting head that includes a means to latch the pilot assembly into the bottom of the auger string and a means to retrieve and lower this assembly with a wireline cable. This device eliminates the use of drill rods with the pilot assembly. The drill rods need only be used with the sample tube.
Henson U.S. Pat. No. 4,081,040 covers a latching mechanism similar to Rassieur U.S. Pat. No. 3,241,624, and also allows the sample tube to be bearingly supported by the latching means so that the tube can protrude through the bottom of the hollow auger head. This is similar to the core barrels mentioned previously except that the inner tube protrudes through the bit and has a cutting edge. As the auger sections and head are turned, the tube is pressed into the ground and the sample forced into the tube. Friction between the tube that protrudes from the auger head and the soil tends to hold the tube stationary so that the augers can revolve around the tube and cut the hole. An advantage of this method is that the auger can be advanced and the sample taken at the same time. The inner rods are eliminated, increasing the speed of the operation. However, there are disadvantages. The tube needs to protrude out the bottom of the auger head a significant distance in order to attempt to prevent the tube from turning as the augers are turned, it being important that the soil sample not be rotated while it is being obtained. In wet, cohesive soil, the sample tends to be sucked out by the vacuum formed when the long tube is pulled up. In stiff material, the farther the tube protrudes out of the head, the more difficult it is to advance the hole. Another disadvantage is that material can force its way between the tube and the auger head causing the tube to rotate as the head and augers rotate, causing a spiraling of the sample and decreasing the sample's usefulness as an undisturbed laboratory sample. Another problem is that frequently material can come into the bottom of the auger string as the sampler is retrieved with the wireline and when reinserting the sampler and latching mechanism, it may not slide all the way to the bottom position, preventing the latching mechanism from functioning.
The problems of obtaining an undisturbed soil sample have been observed for many years. Hansen, U.S. Pat. No. 1,456,983, addressed the problem of keeping a sample tube from rotating, but the device of Hansen is complicated and not well adapted to use in modern drilling rigs.
The soil sampling method and apparatus of this invention, eliminates many of the problems with the wireline method. It allows the sampler to be positioned so that the cutting end is only slightly protruding from the auger head. It provides positive restraint against rotation of the sampling tube, thus eliminating completely the problem of spiraling of the sample. It provides these advantages in a modern drilling rig in which the auger is driven by a rotary table.
One of the objects of this invention is to provide a soil sampling apparatus and method that overcome problems that have been evident in the apparatus and methods known heretofore, in a simple way.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.